Method for reduction of stiction while manipulating micro objects on a surface

ABSTRACT

A system and method reduce stiction while manipulating micro objects on a surface. The system and method employed a field generator configured to generate a driving force at a frequency and amplitude to at least partially overcome stiction between the micro objects and the surface. The field generator is further configured to generate a manipulation force to manipulate the micro objects on the surface in two dimensions. The manipulation force is spatially programmable.

GOVERNMENT FUNDING

This invention was made with Government support under W91CRB-12-C-0006awarded by the Defense Advanced Research Projects Agency (DARPA). Thegovernment has certain rights in this invention.

BACKGROUND

The present application relates generally to micro assemblies. It findsparticular application in conjunction with micro-assembly techniquesused for fabricating micro assemblies, and will be described withparticular reference thereto. However, it is to be appreciated that thepresent application is also amenable to other like applications.

Micro assembly pertains to assembling micro objects into microassemblies. Micro objects are typically a few microns to 100s of micronsin size (e.g., 1-500 microns in length, width or area) and include, forexample, microchips. One technique for micro assembly employselectrostatic or magnetic fields to manipulate micro objects. In thistechnique, patterns are first electrostatically or magnetically encodedon the micro objects. Thereafter, the patterns are used for manipulationof the micro objects in electric or magnetic fields. The patterns canalso be used for identifying and/or matching micro objects, similar tobiological molecular recognition.

One challenge with the above-referenced technique pertains to accuratelymoving micro objects in the presence of stiction. Stiction is thedifference between the coefficient of static friction and dynamicfriction resulting from the intermolecular forces between the twocontacting surfaces. When attempting to move a micro object in thepresence of stiction, the forces required to initiate motion are oftensignificantly greater than the forces required to maintain motion. As aresult, attempts at fine control over the position of a micro objectsubject to stiction often result in ringing, overshoot and instabilitiesin the control.

Another challenge with the above-referenced technique pertains topatterning micro objects. Many different techniques exist forpatterning, including techniques based on chemical means, such asdielectric additives enabling positive or negative charge build up onmicro objects, and techniques based on physical means, such as coronacharging. The known techniques commonly used today can be broken intotwo distinct groups. The first group uses Gyricon bichromal spheres,which develop a dipole when suspended in an electrolyte due to differentzeta potentials of the surfaces of the two hemispheres. The second groupuses electrophoretic ink consisting of two types of oppositely chargingparticles. Known examples of these two groups are believed to use protonexchange based on different acidity levels of the chemical agents.Further, some of these examples are believed to be based ontribocharging. However, tribocharging and proton exchange withelectrolytes are somewhat uncontrolled and immersion in electrolytesleads to complications from ion screening.

A micro assembler employing the above-referenced technique is describedin U.S. Patent App. Pub. No. 2009/0218260. The micro assembler positionsand orients patterned micro objects on an intermediary substrate using aplanar electrode array. Thereafter, the micro objects are transferred toa final substrate for planarization and wiring. This micro assemblerrequires the electrode array to be permanently affixed to the substrateupon which the micro objects are manipulated, thereby necessitating boththe intermediary substrate and the final substrate.

The present application provides new and improved methods and systemswhich improve on the above-referenced technique and address theabove-referenced challenges.

INCORPORATION BY REFERENCE

U.S. patent application No. 14/031,468 for “Direct ElectrostaticAssembly with Capacitively Coupled Electrodes”, by Thompson et al.,filed on Sep. 19, 2013, U.S. Patent Application No. 14/031,529 for“Externally Induced Charge Patterning Using Rectifying Devices”, by Luet al., filed on Sep. 19, 2013, U.S. patent application Ser. No.13/652,194 for “Microchip Charge Patterning”, by Chow et al., filed onOct. 15, 2012, U.S. patent application Ser. No. 12/041,375 (U.S. Pat.No. 7,861,405) for “A System for Forming a Micro-Assembler”, by Chow etal., filed Mar. 3, 2008, U.S. patent application Ser. No. 12/754,245(U.S. Patent App. Pub. No. 2010/0186221) for “Micro-Assembler”, by Chowet al., filed Apr. 5, 2010, U.S. patent application Ser. No. 12/754,230(U.S. Pat. No. 8,181,336) for “Micro-Assembler”, by Chow et al., filedApr. 5, 2010, U.S. patent application Ser. No. 12/754,254 (U.S. Pat. No.8,312,619) for “Micro-Assembler”, by Chow et al., filed Apr. 5, 2010,and U.S. patent application Ser. No. 12/947,004 for “Optically PatternedVirtual Electrodes and Interconnects on Polymers and SemiconductiveSubstrate”, by Lean et al., filed on Nov. 16, 2010, are all incorporatedherein by reference in their entirety.

BRIEF DESCRIPTION

In accordance with one aspect of the present application, a system formanipulating micro objects is provided. The system includes a surfaceupon which the micro objects are manipulated and a field generator. Thefield generator is configured to generate a driving force at a frequencyand amplitude to at least partially overcome stiction between the microobjects and the surface. Further, the field generator is configured togenerate a manipulation force to manipulate the micro objects on thesurface in two dimensions. The manipulation force is spatiallyprogrammable.

In accordance with another aspect of the present application, a methodfor manipulating micro objects is provided. A driving force is generatedat a frequency and amplitude to at least partially overcome stictionbetween the micro objects and a surface upon which the micro objects aremanipulated. Further, a manipulation force to manipulate the microobjects on the surface in two dimensions is generated. The manipulationforce is spatially programmable.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a high level view of a system and a method forforming micro assemblies from micro objects;

FIG. 2A illustrates a side view of a charge patterned micro object;

FIG. 2B illustrates a top view of the charge patterned micro object ofFIG. 2A;

FIG. 3A illustrates a side view of a system for exposing a micro objectto an electric field;

FIG. 3B illustrates a top view of the system of FIG. 3A;

FIG. 4 illustrates a system for exposing a micro object to light;

FIG. 5 illustrates a micro object patterned using a rectifying devicecomprised of a single diode;

FIG. 6 illustrates a micro object patterned using a rectifying devicecomprised of two diodes connected in series;

FIG. 7 illustrates a micro object patterned using a static electricfield;

FIG. 8 illustrates a circuit representing FIG. 5, as well as a graph ofthe simulated surface potentials of multiple points in the circuit;

FIG. 9 illustrates a micro object within which a net charge can develop;

FIG. 10 illustrates a circuit representing FIG. 9, as well as a graph ofthe simulated surface potentials of multiple points in the circuit;

FIG. 11 illustrates a micro object patterned using a rectifying deviceextending between a coupling electrode and the substrate;

FIG. 12 illustrates a circuit representing FIG. 11, as well as a graphof the simulated surface potentials of multiple points in the circuit;

FIG. 13 illustrates a micro object that can develop a complex chargepattern;

FIG. 14 illustrates another micro object that can develop a complexcharge pattern;

FIG. 15 illustrates a micro object patterned across opposing externalsurfaces;

FIG. 16 illustrates another micro object patterned across opposingexternal surfaces;

FIG. 17 illustrates a micro object patterned with a range of chargesbeyond positive and negative;

FIG. 18 illustrates another micro object patterned with a range ofcharges beyond positive and negative;

FIG. 19 illustrates a diode within a micro object;

FIG. 20 illustrates another diode within a micro object;

FIG. 21 illustrates movement of a micro object using an electrode arrayto generate an electric field;

FIG. 22 illustrates the signals driving the electrode array of FIG. 21;

FIG. 23 illustrates superimposing a high frequency driving force over alow frequency manipulation force to generate a composite force;

FIG. 24 illustrates the effect of superimposing a driving force on amanipulation force;

FIG. 25 illustrates a system for positioning and orienting micro objectson a final substrate using an intermediary substrate;

FIG. 26 illustrates a system for positioning and orienting micro objectsdirectly on a final substrate using a static array of electrodes;

FIG. 27 illustrates another system for positioning and orienting themicro objects directly on a final substrate using a moving array ofelectrodes; and

FIG. 28 illustrates a post processing system to complete microassemblies.

DETAILED DESCRIPTION

With reference to FIG. 1, a high level view of a system 10 and a method12 for forming micro assemblies 14 from micro objects 16 are provided.Each micro assembly 14 is formed from one or more micro objects 16.Further, each micro object 16 of a micro assembly 14 is positioned andoriented in a select relationship to the other micro objects 16 of themicro assembly 14. The micro objects 16 are typically microns to 100s ofmicrons in size (e.g., 1-500 microns in length and/or width) and caninclude, for example, microchips. Further, typical fabricationtechniques are employed to generate the micro objects 16.

As illustrated, a micro assembler 18 receives the micro objects 16, andforms the micro assemblies 14 from the micro objects 16. The method 12by which the micro assemblies 14 are formed includes individuallyencoding 20 the micro objects 16 with patterns (i.e., patterning themicro objects 16). Once patterned, the micro objects 16 are positionedand oriented 22 in select relationship to each other on a finalsubstrate using force generating fields, such as electric or magneticfields. Once finally positioned and oriented, the micro objects 16undergo post processing 24 to complete the micro assemblies 14.

Expanding upon FIG. 1, the constituent actions are described in greaterdetail hereafter, beginning with encoding 20 the micro objects 16 withpatterns used for manipulation of the micro objects 16. A pattern of amicro object is a pattern of one or more magnetic or electric poles.Magnetic patterns are used for manipulation of the micro objects 16 inmagnetic fields, and charge patterns are used for manipulation of themicro objects 16 in electric fields. Further, the patterns can be usedfor identifying and/or matching the micro objects 16, similar tobiological molecular recognition. The pattern of a micro object 16 canbe unique to the micro object 16 or unique to a group to which the microobject 16 belongs, such as the type of micro object or the group ofmicro objects forming a specific micro assembly 14.

Any number of well-known techniques can be employed to encode the microobjects 16 with patterns. These include techniques based on chemicalmeans, such as dielectric additives enabling positive or negative chargebuild up on the micro objects 16, and techniques based on physicalmeans, such as corona charging. For example, electrophoretic inkconsisting of two types of oppositely charging particles can be used togenerate charge patterns on the micro objects 16.

In some embodiments, the micro objects 16 are encoded with chargepatterns according to U.S. patent application Ser. No. 13/652,194 for“Microchip Charge Patterning”, by Chow et al., filed on Oct. 15, 2012,incorporated herein by reference. In such embodiments, the micro objects16 include material depositions, which define charge patterns whencharged. The material depositions can be charged before or afterdeposition by, for example, submersion of the material depositions in afluid that causes the charge to develop or through use of an externaldevice, such as a corotron.

FIGS. 2A and 2B provide an example of a charge patterned micro object 50according to U.S. patent application Ser. No. 13/652,194. FIG. 2Aprovides a side view of the charge patterned micro object 50, and FIG.2B provides a top view of the charge patterned micro object 50. Thecharge patterned micro object 50 includes a substrate 52, an insulatinglayer 54 with a first side 56 adjoining the substrate 52, and one ormore material depositions 58 on a second side 60 of the insulating layer54 opposite the first side 56. The substrate 52 carries components ofthe micro object 50, such as electronic components, and the insulatinglayer 54 protects the components of the micro object 50 from thematerial depositions 58. The material depositions 58 define a chargepattern (illustrated as “−++−+−”) when charged.

As an alternative to U.S. patent application Ser. No. 13/652,194, insome embodiments, the micro objects 16 are encoded with charge patternsusing rectifying devices. In such embodiments, the micro objects 16 eachinclude one or more rectifying devices, each rectifying device typicallyconnected to at least one coupling electrode. The rectifying devices,such as diodes or varistors, are any devices that exhibit asymmetriccurrent-voltage (I-V) behavior (i.e., a nonlinear response curve), andthe coupling electrodes are any region where charge can accumulate. Thecoupling electrodes are typically disposed laterally on the microobjects 16 and each coupling electrode can be either explicit orimplicit. An explicit coupling electrode is a region explicitly definedfor the accumulation of charge, and an implicit coupling electrode is aregion that isn't explicitly defined for the accumulation of charge butnonetheless accumulates charge.

To pattern the micro objects 16 when using rectifying devices, charge isinduced to flow through the rectifying devices by a charging system. Thecharging system can use any charging technique resulting in rectifiedcharge build ups. For example, where the rectifying devices of the microobjects 16 are photodiodes, the charging system can induce rectifiedcharge buildups by light incident on the photodiodes. As anotherexample, where the rectifying devices of the micro objects 16 areregular diodes, a field generator of the charging system can inducerectified charge buildups by an electric field alternating (randomly orperiodically) relative to the micro objects 16, such as a direct current(DC) electric field combined with motion of the micro objects 16, or analternating current (AC) electric field. As another example, the fieldgenerator can induce rectified charge buildup by a magnetic field. Theelectric or magnetic field is typically generated by a planar array ofelectrodes or coils, respectively. Further, the electric or magneticfield typically induces charge buildup by capacitive coupling ormagnetic coupling, respectively.

With reference to FIGS. 3A and 3B, a system 100 for exposing a microobject 102 to an electric or magnetic field is provided. FIG. 3Aillustrates a side view of the system 100, and FIG. 3B illustrates a topview of the system 100. While not necessary, the system 100 can be usedas a charging system. Further, as will be seen, the system 100 can beused as a manipulation system.

The system 100 includes a fluid 104 (e.g., a pure dielectric fluid orair) surrounding the micro object 102 and a planar array 106 comprisedof one or more electrodes or coils 108. When the system 100 is beingemployed to generate an electric field, the planar array 106 includeselectrodes, and when the system 100 is being employed to generate amagnetic field, the planar array 106 includes coils. The electrodes orcoils 108 are controlled by one or more programmable power sources 110,such as the illustrated multichannel amplifier, to generate the electricor magnetic field. Further, the electrodes or coils 108 are typicallyarranged in a multi-dimensional grid, such as the illustratedtwo-dimensional grid. The power sources 110 are typically current orvoltage sources, but can also be light sources. Where the power sources110 are light sources, the electrodes or coils 108 are formed fromelectrodes of photosensitive material. Such electrodes or coils can, forexample, be formed according to U.S. patent application Ser. No.12/947,004 for “Optically Patterned Virtual Electrodes and Interconnectson Polymers and Semiconductive Substrate”, by Lean et al., filed on Nov.16, 2010, incorporated herein by reference. The combination of theplanar array 106 and the power sources 110 represents a field generator.

The system 100 further includes a substrate 112 positioned between themicro object 102 and the planar array 106. When the system 100 is beingemployed to generate an electric field, the substrate 112 is aninsulator formed of a polymer, a ceramic, or any other insulatingmaterial through which the electric field can pass. When the system 100is being employed to generate a magnetic field, the substrate 112 is amaterial with a relative magnetic permeability close to one (i.e.,anything non-ferromagnetic or paramagnetic).

With reference to FIG. 4, a system 150 for exposing a micro object 152to light is provided. While not necessary, the system 150 can be used asa charging system. The system 150 includes a fluid 154 (e.g., a puredielectric fluid or air) surrounding a micro object 152 and a substrate156 upon which the micro object 152 rests. Even more, the system 150includes one or more light sources 158 to expose the micro object 152 tolight. The light sources 158 are controlled by one or more power sources160 to illuminate the micro object 152. Further, the light sources 158can be arranged at different locations around the micro object 152and/or may be movable.

With reference to FIG. 5, a micro object 200 patterned using arectifying device 202 is illustrated. The micro object 200 includes asubstrate 204 upon which components (e.g., electrical components) of themicro object 200 are arranged, a first insulator 206 with a first side208 adjoining the substrate 204, two coupling electrodes 210, 212adjoining a second side 214 of the first insulator 206 opposite thefirst side 208, and an optional second insulator 216 adjoining thesecond side 214 around and over the coupling electrodes 210, 212.Capacitive coupling between the substrate 204 and the couplingelectrodes 210, 212 is modeled by capacitors 218, 220.

The micro object 200 further includes the rectifying device 202, whichis connected between the coupling electrodes 210, 212. As illustrated,the rectifying device 202 is a diode, but it is to be appreciated thatthe rectifying device 202 need not be a diode. Rather, the rectifyingdevice 202 need only be a device that exhibits asymmetriccurrent-voltage (I-V) behavior. Further, the rectifying device 202 caninclude a plurality of devices that exhibit asymmetric current-voltage(I-V) behavior. For example, as illustrated in FIG. 6, the rectifyingdevice 202 can be formed of two diodes 222, 224 arranged in series.

With continued reference to FIG. 5, a charging system 226 charges themicro object 200. The charging system 226 can employ any approach tocharge the micro object 200, but the approach typically depends upon thetype of rectifying device of the micro object 200. For example, wherethe rectifying device 202 employs regular diodes, the charging system226 can induce the flow of charge through the rectifying device 202 bygenerating electric fields alternating relative to the micro object 200(e.g., as discussed with FIGS. 3A and 3B). As another example, where therectifying device 202 employs photodiodes, the charging system 226 caninduce the flow of charge through the rectifying device 202 with lightincident on the rectifying device 202 (e.g., as discussed with FIG. 4).

As illustrated, the charging system 226 induces the flow of chargethrough the rectifying device 202 by exposing the micro object 200 to anelectric field alternating relative to the micro object 200. While anyapproach to generating the electric field can be employed, the chargingsystem 226 is illustrated as generating the electric field as describedwith FIGS. 3A and 3B. Hence, the charging system 226 includes a fluid228, such as air or a dielectric liquid, surrounding the micro object200 and a planar electrode array 230 comprising a plurality ofelectrodes 232, 234 driven by one or more voltage sources 236, 238.While not necessary, adjacent electrode pairs can be driven by voltagesources of opposite polarity, as illustrated. The charging system 226further includes an insulator 240 positioned between the micro object200 and the electrode array 230.

When patterning the micro object 200 using the electrode array 230, themicro object 200 is placed adjacent the electrode array 230.Subsequently, the voltage sources 236, 238 of the electrode array 230drive the electrodes 232, 234 with charging signals to produce analternating electric field relative to the micro object 200. Thealternating electric field charges the micro object 200 by capacitivecoupling. Capacitive coupling between the voltage sources 236, 238 andthe coupling electrodes 210, 212 is modeled by capacitors 240, 242, 244,246. The charging signals are typically alternating, such as AC, but canalso be static, such as DC. When the charging signals are static, themicro object 200 moves (e.g., tumbling) relative to the electrode array230, as illustrated in FIG. 7.

With further reference to FIG. 8, a circuit 248 representing the microobject 200 and the charging system 226 is illustrated. Capacitances of10 femtofarads (fF) are used for the coupling capacitors 218, 220, 240,242, 244, 246. Further illustrated is a graph 250 of the simulatedsurface potentials of multiple points in the circuit 248 during andafter the electrode array 230 is driven by charging signals, each beinga 5 cycle burst of 10 kilohertz (kHz) 50 volt (V) sine waves. Thesepoints include: 1) the point intermediate the first coupling capacitor240, labeled as C₁, and the third coupling capacitor 244, labeled as C₃;2) the point intermediate the second coupling capacitor 242, labeled asC₂, and the fourth coupling capacitor 246, labeled as C₄; and 3) thepoint at the anode of the rectifier 202, labeled as diode D₁. As can beseen through review of the graph 250, the charging signals aresufficient to charge the coupling capacitors 218, 220, 240, 242, 244,246 to close to their equilibrium DC offset values.

After the first 0.5 milliseconds (ms) of a charging cycle, the voltagesources 236, 238, labeled as V₁ and V₂, return to zero. However,different electrostatic potentials of about +8V and −8V remain at distalends of the external surface 252 of the micro object 200 through whichthe coupling electrodes 210, 212 capacitively couple to the voltagesources 236, 238. Further, stored charges of about plus and minus 160femtocoulombs (fC) remain on the coupling electrodes 210, 212,respectively. Over time, the induced charge decays because of finiteleakage current, mainly through the rectifier 202. Where the rectifier202 is a diode (as illustrated), leakage is typically low enough thatthe induced charge can maintain at a substantial level many times longerthan the charging signals. For example, for an on-off ratio of 10^6,typical of amorphous silicon diodes, the charge would decay to one halfin approximately 250 seconds.

As known in the art, the induced charge Q of the coupling electrodes210, 212 is related to capacitance C of the coupling electrodes 210, 212and voltage V of the coupling electrodes 210, 212 by the followingequation: Q=CV. By increasing the induced charge Q, the decay time andthe amount of time the charge pattern persists can advantageously beincreased. While numerous approaches exist for increasing the inducedcharge Q, one approach is to increase the voltage V by materialselection of the substrate 204.

The voltage V can be roughly calculated as:

$\begin{matrix}{{{{V_{1} + V_{2}}}*\frac{\frac{1}{c_{5}} + \frac{1}{c_{6}}}{\sum\limits_{i = 1}^{6}\; c_{i}}},} & (1)\end{matrix}$where V₁, V₂, C₁, C₂, C₃, and C₄ are as described above, and C₅ and C₆represent the fifth coupling capacitor 218 and the sixth couplingcapacitor 220, respectively. Hence, the voltage V developed on thecoupling electrodes 210, 212 increases as the fifth coupling capacitor218 and the sixth coupling capacitor 220 become smaller. When thesubstrate 204 is formed from a conductive material, such as silicon(Si), as opposed to an insulating substrate, such as glass or sapphire,the fifth and sixth coupling capacitors 218, 220 are greater, wherebythe voltage V is greater when the substrate 204 is insulating.

As shown in FIGS. 5-7, the coupling electrodes 232 are isolated from thesurrounding environment by the second insulator 216. This advantageouslyminimizes the charge leakage path and increases the length of time theinduced charge can be stored. However, charge conservation law alsoeliminates the possibility of inducing any net charge. FIG. 9illustrates an embodiment of the micro object 200 that can result in anet induced charge. In contrast with the previous embodiments of themicro object 200, this embodiment includes the second insulator 216 andfurther includes a small opening 254 in the second insulator 216allowing the external environment of the micro object 200 (e.g., adielectric fluid carrying charge director molecules or other ions) tocome in contact with one of the coupling electrodes 210, 212.

With reference to FIG. 10, an embodiment of the circuit 248corresponding to FIG. 9 is provided. The circuit 248 includes a resistor256, labeled as R₁, representing the small opening 254. The resistor 256includes a high resistance of approximately 10^11 Ohms and extends fromthe adjacent electrode to ground. Further illustrated in FIG. 10 is anembodiment of the graph 250 corresponding to this embodiment of thecircuit 248. As can be seen through review of the graph 250, after thefirst 0.5 ms of the charging cycle, the voltage sources 236, 238 returnto zero. However, different electrostatic potentials of about +11V and−5V remain at distal ends of the external surface 252 of the microobject 200 through which the coupling electrodes 210, 212 capacitivelycouple to the voltage sources 236, 238. Further, a net charge of about200 fC is stored on the coupling electrodes 236, 238.

With reference to FIG. 11, another embodiment of the micro object 200 isillustrated. In contrast with the previous embodiments of the microobject 200, the substrate 204 is semi conductive. Further, therectifying device 202 is connected between one of the electrodes 210,212 and the substrate 204. The other electrode is left floating (i.e.,not connected to the rectifying device 204).

With reference to FIG. 12 an embodiment of the circuit 248 correspondingto FIG. 11, as well as embodiment of the graph 250 corresponding to thisembodiment of the circuit 248, are provided. As can be seen throughreview of the graph, after the first 0.5 ms of the charging cycle, thevoltage sources 236, 238 return to zero but different electrostaticpotentials of about +3.5V and −3.5V remain at distal ends of theexternal surface 252 of the micro object 200 through which the couplingelectrodes 210, 212 capacitively couple to the voltage sources 236, 238.Hence, the embodiment of the micro object 200 of FIG. 12 is lesseffective at charge build compared to the embodiment of the micro object200 of FIG. 5. However, the embodiment of FIG. 12 may be easier toimplement.

The foregoing embodiments of the micro object 200 illustrated differentapproaches to forming a simple dipole (i.e., two poles) on the externalsurface 252 of the micro object 200 through which the couplingelectrodes 210, 212 capacitively couple to the voltage sources 236, 238.These approaches can be extended to create a complex charge pattern(i.e., more than two poles) on the external surface 252 by including aplurality of rectifier-electrode pairs, which can be overlapping. Arectifier-electrode pair is a pair of a rectifying device and one ormore electrodes. Each rectifier-electrode pair includes a rectifyingdevice either spanning between an electrode pair or spanning from anelectrode to the substrate 204.

With reference to FIG. 13, an embodiment of the micro object 200 thatcan develop a complex charge pattern is provided. The micro object 200includes a plurality of rectifying devices 258, 260, 262, 264, 266(illustrated as diodes). Each rectifying device 258, 260, 262, 264, 266extends from a different electrode 268, 270, 272, 274, 276 to thesubstrate 204, which is necessarily conductive or semi conductive. Inother words, the micro object 200 includes a plurality ofrectifier-electrode pairs, each pair being a pair of a rectifying deviceand a single electrode. To change the charge contributed to the externalsurface 252 by one of the rectifying devices 258, 260, 262, 264, 266,the bias of the rectifying devices can be changed. Advantageously, thisembodiment of the micro object 200 offers a high degree of flexibilityin terms of designing the charge pattern.

With reference to FIG. 14, another embodiment of the micro object 200that can develop a complex charge pattern is provided. The micro object200 includes a single rectifying device 278 paired with a plurality ofelectrodes 280, 282, 284, 286, 288, 290. In other words, the microobject 200 includes a plurality of overlapping, but unique,rectifier-electrode pairs, each pair being a pair of the rectifyingdevice 278 and an electrode pair. Advantageously, this embodiment of themicro object 200 minimizes the number of active devices (i.e.,rectifying devices) needed.

The foregoing embodiments of the micro object 200 dealt with forming acharge pattern on the external surface 252 through which the couplingelectrodes capacitively couple to the voltage sources 236, 238. However,the previously described approaches to forming a charge pattern can beextended to create charge patterns that span opposing external surfacesof the micro object 200.

With reference to FIG. 15, an embodiment of the micro object 200patterned across opposing external surfaces 252, 290 is provided. Incontrast with the embodiment of the micro object 200 of FIG. 5, thisembodiment of the micro object 200 includes only the first electrode 210and the rectifying device 202 is connected between the electrode 210 andthe substrate 204, which is necessarily conductive or semi conductive.After charging, the micro object 200 includes a first charge on theexternal surface 252 of the micro object through which the micro object200 capacitively couples to the voltage sources 236, 238. Further, themicro object 200 includes a second charge on the opposing externalsurface 290 of the micro object 200. Hence, a charge pattern along thethickness of the micro object 200 (i.e., the Z direction) is created,which can be useful for aligning the micro object 200 facing up orfacing down.

With reference to FIG. 16, another embodiment of the micro object 200patterned across opposing external surfaces 252, 290 is provided. Themicro object 200 includes the substrate 204, two insulators 292, 294adjoining opposite sides 296, 298 of the substrate 204, two couplingelectrodes 300, 302, 304, 306 adjoining each of the two insulators 292,294 opposite the substrate 204, and two optional second insulators 308,310 adjoining the two insulators 292, 294 around and over the couplingelectrodes 300, 302, 304, 306. Each coupling electrode 300, 302, 304,306 is connected with another electrode 300, 302, 304, 306 on anopposite side of the substrate 204 and a common side of the micro object200. The micro object 200 further includes two oppositely biasedrectifying devices 312, 314, each connected from a different couplingelectrode 304, 306 on a common side of the substrate 204 to thesubstrate 204, which is conductive or semi conductive.

After charging the micro object 200, the micro object 200 includes adipole on the external surface 252 of the micro object 200 through whichthe coupling electrodes 300, 302, 304, 306 are capacitively coupled tothe voltage sources 236, 238. Further, the micro object 200 includes asecond dipole on the opposite external surface 290 of the micro object200. Hence, the micro object 200 includes dipoles on opposing externalsurfaces 252, 290. More complex charge patterns can be created inaccordance with the teachings of this embodiment by including additionalcoupling electrodes and rectifying devices, similar to the embodiment ofFIG. 11.

The foregoing embodiments of the micro object 200 dealt with binarycharge patterns (i.e., charge patterns of positive and negative chargeof fixed quantities). Charge patterns comprised of a range of chargesbeyond just positive and negative fixed quantities can be employed bylaterally varying the thickness of the insulators and/or by varying thearea of the coupling electrodes.

With reference to FIG. 17, an embodiment of the micro object 200patterned with a range of charges beyond positive and negative isprovided. The micro object 200 is the same as the embodiment of FIG. 5except that the coupling electrodes 210, 212 vary in area. By varyingthe area of the coupling electrodes 210, 212, the capacitances of thecoupling capacitors 218, 220, 240, 242, 244, 246 vary. Namely, thecoupling capacitors 218, 240, 244 of the first coupling electrode 210are different than the coupling capacitance of 220, 242, 246 of thesecond coupling electrode 212.

With reference to FIG. 18, another embodiment of the micro object 200patterned with a range of charges beyond positive and negative isprovided. The micro object 200 is the same as the embodiment of FIG. 5except that the thickness of the second insulator 216 varies laterally.Similar to varying the area of the coupling electrodes 210, 212, varyingthe thickness of the second insulator 216 varies the capacitances of thecoupling capacitors 218, 220, 240, 242, 244, 246. Hence, the couplingcapacitors 218, 240, 244 of the first coupling electrode 210 aredifferent than the coupling capacitance of 220, 242, 246 of the secondcoupling electrode 212.

The foregoing embodiments of the micro object 200 conceptuallyillustrated the rectifying devices 202, 258, 260, 262, 264, 266, 278,312, 314 as diodes. Any number of well-known approaches to formingdiodes can be employed. However, two embodiments of a diode 316 aredescribed in FIGS. 19 and 20.

With reference to FIG. 19, an embodiment of the diode 316 is illustratedas the rectifying device 202 of the embodiment of the micro object 200of FIG. 5. According to this embodiment of the diode 316, the diode 316is created using thin film (e.g., fractions of a nanometer to severalmicrometers thick) electronic technology. As illustrated, the diode 316is the well-established a-Si:H PIN diode structure, but other thin filmelectronic technologies can be used, such as printed organic diodes,Schottky diodes formed with metal and a thin film semiconductormaterial, such as indium-gallium-zinc oxide (InGaZnO), copper oxide(CuO), cadmium selenide (CdSe), gallium indium zinc oxide (GIZO), orsome other semiconducting metal oxide or polymeric material. The diode316 includes an insulator 318 with a p-type semiconductor 320 and ann-type semiconductor 322 on opposite sides. Further, the couplingelectrodes 210, 212 are connected to the semiconductors 320, 322 byconductors 324, 326.

With reference to FIG. 20, another embodiment of the diode 316 isillustrated as the rectifying device 202 of the embodiment of the microobject 200 of FIG. 11. According to this embodiment of the diode 316, avia 328 through the insulator 206 connects one of the couplingelectrodes 212 to the substrate 204, which is often semi conducting.Where the substrate 204 is semi conducting, the diode 316 can be formedon the substrate 204 (e.g., using the a-Si:H PIN diode structure) orformed by contacting the substrate 204 with the coupling electrode 212(i.e., a simple Schottky diode), as illustrated.

The previous embodiments of the micro object 200 and the diode 316 arenot intended to be exhaustive. Rather, the previous embodiments areintended to illustrate the different design decisions that can be madewhen designing the micro object 200. Such design decisions includedetermining whether the micro object 200 is to include a simple chargepattern (e.g., as shown in FIG. 5) or a complex charge pattern (e.g., asshown in FIG. 13). When a simple charge pattern is desired, the microobject 200 includes a single rectifier-electrode pair. When a complexcharge pattern is desired, the micro object 200 includes a plurality ofrectifier-electrode pairs. The design decisions further includedetermining the location of charge buildup on the micro object 200(c.f., FIG. 5 and FIG. 15).

For each rectifier-electrode pair, a determination is made as to: 1)whether the rectifying device should include one or more active devices(c.f., FIG. 5 and FIG. 6); 2) whether the rectifying device shouldextend between coupling electrodes (e.g., as shown in FIG. 5) or betweena coupling electrode and the substrate 204 (e.g., as shown in FIG. 11);3) whether a coupling electrode should be exposed to the external fluid(e.g., as shown in FIG. 9); 4) whether the charge should include onlypositive or negative charge (e.g., as shown in FIG. 15) or a range ofcharge (e.g., as shown in FIG. 17); and 5) the design of the rectifyingdevices, examples of which are shown in FIGS. 19 and 20.

Advantageously, the foregoing approaches to using rectifying devices forpatterning micro objects can be more predictable and reliable comparedto other charging mechanisms. The foregoing approaches are based onsimple circuit techniques and remove the vagaries of chemical chargeformation, micelle formation, and so on. The foregoing approaches tousing rectifying devices also allow the use of pure dielectric fluids orair as the surrounding medium. This has the advantage of long Debyelengths, removal of field decay from ion transport and screening, andlow sensitivity to moisture.

Referring back to the high level system 10 and method 12 of FIG. 1,after the micro objects 16 (also identified herein as micro objects 102,152, 200) are individually encoded 20 with patterns, the micro objects16 are positioned and oriented 22 on a final substrate by a manipulationsystem. The manipulation system varies force fields, such as electric ormagnetic fields, in both space and time to move the micro objects 16. Asshould be appreciated, magnetic or electric poles of like polarityrepel, whereas magnetic or electric poles of opposite polarity attract.On this basis, generating and/or moving corresponding patterns of themicro objects 16 allows the micro objects 16 to be selectivelymanipulated. A corresponding pattern of a micro object describes theopposite pattern (i.e., opposite of each pole) of the micro object andhence attracts the micro object. In some embodiments, depending upon theapproach used to pattern the micro objects 16, the same system can beemployed to both pattern the micro objects 16 and move the micro objects16 to the desired position and orientation.

Any number of well-known approaches can be employed to move the microobjects 16. When the micro objects 16 are charge patterned, an array ofelectrodes is typically employed. For example, with reference to FIGS.3A and 3B, the system 100 described therein can additionally oralternatively be employed to move the micro objects 16 using the planararray 106 with electrodes. When the micro objects 16 are magneticallypatterned, an array of coils (e.g., an array of wire windings) istypically employed. For example, with reference to FIGS. 3A and 3B, thesystem 100 described therein can additionally or alternatively beemployed to move the micro objects 16 using the planar array 106 withcoils.

Where the system 100 of FIGS. 3A and 3B is employed as a manipulationsystem, a micro object 102 is placed adjacent the planar array 106within the fluid 104 before movement of the micro object 102. When themicro object is charge patterned, as opposed to magnetically patterned,the fluid is typically a dielectric fluid (e.g. Isopar) with a smallamount of surfactant added (e.g. docusate sodium (AOT)) to increase theelectrical conductivity of the fluid 104. Further, before movement ofthe micro object 102, the power sources 110 can optionally drive theplanar array 106 with charging signals to charge or recharge the microobject 102. Subsequent to placing the micro object 102 in the fluid 104and assuming the micro object 102 is charged, the power sources 110drive the electrodes or coils 108 with manipulation signals to move themicro object 102. The manipulation signals can, for example, move themicro object 102 to its selected location by moving the correspondingpattern complementary to the pattern on the micro object 102 across thesubstrate 112.

With reference to FIG. 21, movement of the embodiment of the microobject 200 of FIG. 5 is illustrated. Other embodiments of the microobject 200 can similarly be moved. Movement of the micro object 200 isperformed by a manipulation system 330 using an electrode array 232comprised of a plurality of electrodes 334, 336, 338, 340, eachcontrolled by a voltage source 342, 344, 346, 348. Before movement ofthe micro object 200, the micro object 200 is placed in a dielectricfluid 350 adjacent the electrode array 232 and separated from theelectrode array 232 by an insulator 352. Further, the micro object 200is optionally charged or recharged using the electrode array 232.Thereafter, the electrode array 232 is driven to move the micro object200 to the left.

FIG. 22 provides an example of the signals that can be produced by thevoltage sources 342, 344, 346, 348 to move the micro object 200 to theleft. These signals include both charging signals and manipulationsignals. During the first 0.5 ms, charging signals charge or rechargethe micro object 200 using a 5 cycle burst of approximately 10 kHz 50 Vsine waves. As should be appreciated, this is the charging signaldescribed above for charging micro objects employing rectifiers. Aftercharging, manipulation signals move the micro object 200 on the surfaceof the insulator 352 to the left.

Referring back to FIG. 1, accurate movement of the micro objects 16 isimportant to generating the micro assemblies 14. However, a challengewith accurately moving objects over a surface, such as a substrate, isovercoming stiction. Stiction is the difference between the coefficientof static friction, and dynamic friction, resulting from theintermolecular forces between the two surfaces in contact. Whenattempting to move a micro object in the presence of stiction, theforces required to initiate motion are often significantly greater thanthe forces required to maintain motion. As a result, attempts at finecontrol over the position of a micro object subject to stiction oftenresult in ringing, overshoot and instabilities in position control.

A solution to overcoming stiction is to apply a high frequency drivingforce (e.g., a high frequency, periodic driving force) to the microobjects 16. The frequency of the driving force is high (e.g., amagnitude greater) compared to the frequency of the desired net motion(i.e., the desired speed). The amplitude of the driving force is chosenso that the peak force is sufficient to overcome stiction, and thefrequency of the driving force is chosen so that the displacement of amicro object during one cycle is less than the desired assemblyprecision.

This solution can be applied to obtain precise control over the motionof the micro objects 16 during manipulation by superimposing a highfrequency driving force 400 over a low frequency manipulation force 402to generate a composite force 404. The frequency of the manipulationforce is low compared to the frequency of the driving force. Themanipulation force 402 is spatially programmable in that it can beprogrammatically moved to move micro objects. The composite force isthen applied to the micro objects 16 as an electric or magnetic fieldusing a field generator. For example, a voltage representation of thecomposite force can be applied to the planar array 106 of FIGS. 3A and3B by the power sources 110 of FIGS. 3A and 3B.

In some embodiments, the frequency and amplitude of the driving forceare chosen to only partially overcome stiction related forces so themanipulation force is also needed to move the micro objects 16. In suchembodiments, the frequency and amplitude are typically chosen so thatwhen the manipulation force is superimposed, the dynamics of the microobjects 16 are altered to increase or decrease the effective amount ofdamping.

With reference to FIG. 24, the effect of a driving force is illustrated.The dark curve 410 represents a manipulation force as a 150 V sinusoidalvoltage waveform at a frequency of 0.5 hertz (Hz). The manipulationforce moves a micro object back and forth between two electrodes. Theother curve 412 is the measured velocity of a micro object in responseto the composite force. During roughly the first 12 seconds, only themanipulation force is applied. Thereafter, at approximately 12 seconds,a driving force is superimposed over the manipulation force. The drivingforce is represented as a 150 V sinusoidal voltage waveform at afrequency of 330 Hz. As can be seen, without the driving force, themicro object only moves when the manipulation force is high (i.e., theamplitude is high). In contrast, with the driving force, the velocity ofthe micro object tracks the composite force except for a phase lag. Thephase lag is present due to the capacitive coupling between the driveelectrodes and the dielectric fluid within which the micro object ispositioned.

Referring back to FIG. 1, during manipulation of the micro objects 16,the driving force can be globally controlled for all of the microobjects 16 or locally controlled to selectively alter the mobility ofindividual micro objects. For example, where a micro object has alreadybeen moved to its predetermined assembly location, the micro object canbe reversibly lock in place by not applying the driving force to themicro object. When the manipulation force is applied using an array orcoils or electrodes, this can be achieved by suppressing application ofthe driving force to electrodes proximate the micro objects to bereversibly locked.

Further, during manipulation of the micro objects 16, net motion of themicro objects 16 can be achieved by a combination of a periodicmanipulation force and a driving force. In some embodiments, the drivingforce can be applied as a step change in force, as a short step pulse,briefly before application of a manipulation force, or during part of acycle of a manipulation force. Further, in some embodiments, the drivingforce can be integrated with the manipulation force. That is to say, themanipulation force includes components during part of its cycles thatrepresent the driving force.

One example of achieving net motion is to apply a manipulation forcewith a periodic field to the micro objects 16 and superimpose a drivingforce during only part (e.g., half) of a cycle of the manipulationforce. Another example of achieving net motion is to apply asymmetricperiodic force to the micro objects 16, such as a saw tooth waveform.One cycle of a saw tooth waveform consists of a step increase in force,followed by a linear ramp down back to the initial force. The stepincrease contains high frequency components that reduce stictionresulting in motion. If the ramp back down to the initial force is slowenough, the micro objects stick onto the surface again.

The driving force can be applied by a field generator to micro objectsusing any approach to generating an electric or magnetic field. However,an array of electrodes or coils driven by a voltage representation ofthe driving force is typically employed. An electrode array can beemployed to generate the driving force as an electric field, and a coilarray can be employed to generate the driving force as a magnetic field.The electrode array can be formed of traditional electrodes orphotosensitive electrodes, as described in connection with FIGS. 3A and3B. Where an array of coils or electrodes is employed to generate thedriving force, the driving force can be applied to only to specificelectrodes or coils that are proximate micro objects to be manipulated.Further, in some embodiments, the same coil or electrode can be employedto generate both the manipulation force and the driving force.Alternatively, in other embodiments, the manipulation force is generatedby different coils or electrodes than the coils or electrodes generatingthe manipulation force.

The foregoing approaches to manipulating the micro objects 16 have thusfar been limited to moving the micro objects 16 in electric or magneticfields. There has been limited discussion on positioning and orientingthe micro objects 16 on a final substrate. Even so, it is to beappreciated that, in some embodiments, the foregoing approaches tomanipulating the micro objects 16 can be used exclusively to positionand orient the micro objects 16 on the final substrate. For example, thefinal substrate can be insulating and positioned between the microobjects 16 and an electrode array. The electrode array then positionsthe micro objects using electric fields, as described above. In otherembodiments, the micro objects 16 are moved to the final substratethrough a combination of electric or magnetic fields, and mechanicalforce.

In some embodiments, the patterned micro objects 16 are positioned andoriented on a final substrate using both electric or magnetic fields,and mechanical force, according to U.S. patent application Ser. No.12/754,245 (U.S. Patent App. Pub. No. 2010/0186221) for“Micro-Assembler”, by Chow et al., filed Apr. 5, 2010, incorporatedherein by reference. According to U.S. patent application Ser. No.12/754,245, the micro objects 16 are first positioned and oriented on anintermediary substrate by charge or magnetic patterns encoded on theintermediary substrate using a planar electrode array permanentlyaffixed to the intermediary substrate. Thereafter, the positioned andoriented micro objects 16 are mechanically transferred to the finalsubstrate in a manner that preserves their relative positions andorientations.

With reference to FIG. 25, a manipulation system 450 according U.S.patent application Ser. No. 12/754,245 is provided. As illustrated,patterned micro objects 452 are placed in a reservoir 454 where themicro objects 452 are stored prior to assembly. The reservoir 454 istypically a bath of fluid (e.g., a dielectric fluid with chargedadditives to allow finite conductivity) within which the micro objects452 are randomly positioned and oriented. However, other approaches tostoring the micro objects 452 prior to assembly are contemplated.

A transporter 456 receives micro objects from the reservoir 454 andtransfers the micro objects away from the reservoir 454 using atraveling wave pattern created by electrodes on plate 458. The plate 458is typically an insulator. While receiving the micro objects, thetransporter 456 positions and orients the micro objects on the plate 458using magnetic or charge patterns on the plate 458 that correspond tothe magnetic or charge patterns of the micro objects. Where a microobject is encoded with a pattern, a corresponding pattern on the plate458 attracts the micro object to the plate 458, while at the same timeorienting and positioning the micro object relative to the correspondingcharge pattern on the plate 458.

To generate the patterns on the plate 458, a field generator 460 isemployed. The field generator 460 includes a planar array 462 ofelectrodes or coils permanently affixed to the plate 458 opposite themicro objects 452. The planar array 462 is driven by programmable powersources of the field generator 460, such as programmable voltagesources. Typically, the planar array 462 is two-dimensional. Where themicro objects 452 are magnetically patterned, the planar array 462includes coils, and where the micro objects 452 are charge patterned,the planar array 462 includes electrodes. The field generator 460 canalso expose the micro objects 452 to the driving force to overcomestiction and better facilitate alignment of the micro objects.

A photoconductor 464, such as a cylindrical photoconductor, optionallyreceives micro objects from the transporter 456. As discussed above,these micro objects are arranged in known positions and orientations.While not necessary, the photoconductor 464 can be patterned to betterposition and orient the micro objects received from the transporter 456.This charging can, for example, be performed by an optical patternwriter 466, such as a laser printer raster output scanner (ROS), or by aplanar electromagnetic array.

By way of the photoconductor 464, positioned and oriented micro objectsare transferred to a final substrate 468 at a transfer region 470. Whilenot necessary, the final substrate 468 is preferably non-stationary,which can advantageously aid in achieving proper positioning of themicro objects on the final substrate 468. After transfer of the microobjects on the photoconductor 464 to the final substrate 468, the microobjects are finally placed and oriented.

Through experiments studying the dynamics of micro objects in responseto electric fields, it was determined that an insulator intermediate anelectrode array and micro objects is necessary to prevent chargetransfer between the micro objects and the electrodes. However, it wasalso determined that the insulator does not need to be permanentlyaffixed to the electrode array. Experiments have successfullymanipulated micro objects with electrodes that were insulated by simplyplacing a piece of microscope cover glass or a plastic film on top ofthe electrodes without any adhesives or bonding steps.

Referring back to FIG. 1, as an alternative to U.S. patent applicationSer. No. 12/754,245, in some embodiments, the micro objects 16 arepositioned and oriented directly on a substrate that is not permanently(i.e., impermanently) affixed to the field generator. Thisadvantageously allows the micro objects 16 to be directly positioned andoriented on the final substrate. In contrast, U.S. patent applicationSer. No. 12/754,245 has the micro objects 16 positioned and oriented onan intermediary substrate before transfer to the final substrate.Notwithstanding that it is advantageous to directly position and orientthe micro objects 16 directly on the final substrate, it is to beappreciated that the micro objects 16 can still be indirectly positionedand oriented on the final substrate. This can, for example, be performedin the same manner as U.S. patent application Ser. No. 12/754,245 withthe main differences being that the field generator is not bepermanently affixed to the transporter.

With reference to FIGS. 26 and 27, a manipulation system 500 positioningmicro objects 502 on an insulating substrate 504 that is not permanentlyaffixed to a field generator 506 is provided. The field generator 506employs electric or magnetic fields to manipulate the micro objects 502depending upon whether the micro objects 502 are charge patterned ormagnetically patterned. As illustrated, the field generator 506 employsan array 508 of electrodes or coils 510 to generate the electric ormagnetic fields, as described above (e.g., with FIGS. 3A and 3B). Theplanar array 508 is driven by programmable power sources of the fieldgenerator 506, such as programmable voltage sources. Further, the array508 is typically two-dimensional.

The substrate 504 is fed over the electric or magnetic fields producedby the field generator 506 from storage. As illustrated, the substrates504 is stored on a drum or roll 512 and fed over the array 508. Thefield generator 506 can remain fixed relative to the substrate 504, asillustrated by the fixed position of the array 508 in FIG. 26.Alternatively, the field generator 506 can move with the substrate 504to reduce wear on the field generator 506 (e.g., by a embedding at leastpart of the field generator 506 in a flexible conveyer belt 514, or on adrum), as illustrated by the array 508 embedded with the conveyer belt514 of FIG. 27. Further, a fluid 516, such as a dielectric fluid,typically covers the substrate 504 opposite the field generator 506.

As the substrate 504 is fed over the electric or magnetic fields, therandomly arranged micro objects 502 are added to the fluid 516 or thesurface of the substrate 504 opposite the field generator 506.Concurrently therewith, the field generator 506 generates electric ormagnetic fields to position and orient the micro objects 502 on thesubstrate 504 into pre-defined patterns, optionally after charging orrecharging the micro objects 502. For example, the illustrated array 508can be controlled by power sources to generate manipulation signals, andoptionally driving signals to reduce stiction and/or charging signals tocharge or recharge the micro objects 502. Typically, the micro objects502 are positioned and oriented by generating corresponding patterns onthe substrate 504 using the field generator 506.

Referring back to FIG. 1, after the micro objects 16 are positioned andoriented 22 on the final substrate, the micro objects 16 undergo postprocessing 24 by a post processing system. Post processing typicallyincludes one or more of fixing the micro objects 16 to the finalsubstrate, planarizing the micro objects 16, and wiring the microobjects 16. Fixation, planarization and wiring can be achieved throughany number of well-known means. Further, fixation, planarization andwiring can be achieved at the same location where the micro objects 16are arranged, at a separate location, or spread between a plurality oflocations, which can include the location where the micro objects 16 arearranged.

Fixation can, for example, be achieved using a monomer solution of alight curable polymer as a dielectric fluid within which the microobjects 16 are arranged on the final substrate. Once micro objects arearranged on the final substrate, light is directed to the regionsadjacent the micro objects to initiate polymerization and thereby fixthe micro objects to the final substrate. As another example, fixationcan be achieved by thermally fusing the micro objects 16 to the finalsubstrate. With a polymer substrate, the area of the substrate uponwhich a micro object is positioned and oriented is locally heated andmelted to fix the micro object in place. Local heating can, for example,be accomplished by focusing an infrared laser on the area. As anotherexample, fixation can be achieved by adhering the micro objects 16 tothe final substrate with an adhesive. With an adhesive, the adhesive islocally cured around the micro objects 16. As another example, fixationcan be achieved by embossing the micro objects 16 into the finalsubstrate. As another example, fixation can be achieved throughlocalized curing of an adhesive. Planarization can, for example, beachieved by embossing, or spin coating a polymer over the micro objects16 and the final substrate. Wiring can, for example, be achieved byphoto patterning metal wires or inkjet printing metal lines.

In some embodiments, after fixing micro objects to any given region ofthe final substrate, but before these micro objects are planarized andwired, the region is passed over the electric and magnetic fieldsgenerated by the manipulation system again, thereby allowing additionalmicro objects to be fixed to the region. This loop of positioning andorienting micro objects on a region of a final substrate, followed byfixing these micro objects to the region, can be performed one or moretimes to increase the fill factor and generate different types of microassemblies. For example, the final substrate can be divided into aplurality of region, each corresponding to a specific micro assembly.The number of times the above described loop is performed for each ofthese regions then depends upon the specific micro assembly of theregion. Once looping is complete for a region, the micro objects of theregion can undergo planarization and wiring.

With reference to FIG. 28, an example of a post processing system 550 isprovided. The post process system 550 receives a final substrate 552upon which micro objects 554 are positioned and oriented, and fixes themicro objects 16 to the final substrate 552 using a fixation device 556.Numerous approaches can be employed to fix the micro objects 554.However, as illustrated, the fixation device 556 fixates the microobjects 554 to the final substrate 552 using infrared light directed tothe regions adjacent the micro objects 554. The infrared light locallyheats and melts the regions of the final substrate 552 upon which themicro objects 554 are positioned. When the regions of the finalsubstrate 552 cool, the micro objects 554 become fixed to the finalsubstrate 552.

It will be appreciated that variants of the above-disclosed and otherfeatures and functions, or alternatives thereof, may be combined intomany other different systems or applications. Various presentlyunforeseen or unanticipated alternatives, modifications, variations orimprovements therein may be subsequently made by those skilled in theart which are also intended to be encompassed by the following claims.

What is claimed is:
 1. A system for manipulating micro objects, thesystem comprising: a surface upon which the micro objects aremanipulated; and a field generator configured to: generate a drivingforce at a frequency and amplitude to at least partially overcomestiction between the micro objects and the surface; and generate amanipulation force to manipulate the micro objects on the surface in twodimensions, the manipulation force being spatially programmable.
 2. Thesystem of claim 1, wherein the micro objects are 1 to 500 microns insize.
 3. The system of claim 1, wherein the field generator is furtherconfigured to: superimpose the driving force on the manipulation forceto achieve motion of the micro objects.
 4. The system of claim 3,wherein the driving force is superimposed on the manipulation forceduring only part of the manipulation force.
 5. The system of claim 3,wherein the frequency and the amplitude of the driving force onlypartially overcomes stiction between the micro objects and the surface.6. The system of claim 5, wherein the frequency and amplitude of thedriving force control the amount of damping when the driving force issuperimposed on the manipulation force.
 7. The system of claim 1,wherein the frequency of the driving force is at least an order ofmagnitude greater than the frequency of the manipulation force.
 8. Thesystem of claim 1, wherein the driving force is a repeating step changein force or a repeating step pulse.
 9. The system of claim 1, whereinthe field generator is further configured to: apply the driving force tothe micro objects; and apply the manipulation force to the micro objectsafter applying the driving force to the micro objects.
 10. The system ofclaim 1, wherein the manipulation force includes frequency components atleast an order of magnitude greater than the frequency of themanipulation force for only part of the manipulation source.
 11. Thesystem of claim 1, wherein the field generator is further configured to:apply the driving force to only a subset of the micro objects.
 12. Thesystem of claim 1, wherein the field generator is further configured to:apply the driving force to the micro objects as an electric field. 13.The system of claim 12, further including: a two-dimensional array ofelectrodes used to generate the electric field.
 14. The system of claim13, wherein the field generator applies the driving force to the microobjects using a first set of electrodes of the array, and wherein thefield generator is further configured to: apply the manipulation forceto the micro objects as an electric field using a second set ofelectrodes of the array, the second set of electrodes different than thefirst set.
 15. The system of claim 13, wherein the field generatorapplies the driving force to the micro objects using a first set ofelectrodes of the array, and wherein the field generator is furtherconfigured to: apply the manipulation force to the micro objects as anelectric field using a second set of electrodes of the array, the secondset of electrodes the same as the first set.
 16. The system of claim 12,further including: one or more photosensitive electrodes generating theelectric field.
 17. The system of claim 1, wherein the manipulationsystem is further configured to: apply the driving force to the microobjects as a magnetic field.
 18. The system of claim 17, furtherincluding: a two-dimensional array of coils used to generate themagnetic field.
 19. The system of claim 18, wherein the field generatorapplies the driving force to the micro objects using a first set ofcoils of the array, and wherein the field generator is furtherconfigured to: apply the manipulation force to the micro objects as amagnetic field using a second set of coils of the array, the second setof coils different than the first set.
 20. The system of claim 18,wherein the field generator applies the driving force to the microobjects using a first set of coils of the array, and wherein the fieldgenerator is further configured to: apply the manipulation force to themicro objects as a magnetic field using a second set of coils of thearray, the second set of coils the same as the first set.
 21. A methodfor manipulating micro objects, the method comprising: generating adriving force at a frequency and amplitude to at least partiallyovercome stiction between the micro objects and a surface upon which themicro objects are manipulated; and generating a manipulation force tomanipulate the micro objects on the surface in two dimensions, themanipulation force being spatially programmable, wherein the drivingforce and the manipulation force are generated by a field generator. 22.The method of claim 21, wherein the micro objects are 1 microns to 500microns in size.
 23. The method of claim 21, further including:superimposing the driving force on the manipulation force to achievemotion of the micro objects.
 24. The method of claim 21, furtherincluding: applying the driving force to only a subset of the microobjects.
 25. The method of claim 21, further including: apply thedriving force to the micro objects as an electric field using atwo-dimensional array of electrodes.
 26. The system of claim 21, furtherincluding: apply the driving force to the micro objects as a magneticfield using a two-dimensional array of coils.